Week 6 - Acid Base Flashcards
(21 cards)
What will alkaline is result in?
Lowers free calcium by causing calcium ions to precipitate out of solution. Results in parasthesia and tetany
What are the results of acidaemia
Increases plasma potassium ion concentration which effects excitability resulting in arrhythmia. The increased hydrogen ions denatures proteins which affects muscle contractility and hepatic function
How is plasma ph determined?
Ratio if HCO3 to pCo2 Henderson hesselbachs equation - look at it because it’s too hard to type
What is the effect of hyperventilation
Hyperventilation causes more co2 to be blown off therefore hypocapnia resulting in equilibrium shifting to the left resulting in higher ph which is respiratory alkalaemia
What happens with hypo ventilation
Decreased co2 blown off = equilibrium shifts to the left = more hydrogen ions = lower ph and respiratory acidosis
How are carbon dioxide levels controlled?
Tight regulation via chemoreceptors in the periphery and centrally. Central ones can’t detect change in ph as H ions can’t cross blood brain barrier but they can detect change in co2 and have th biggest effect, slower but account for 80%
Where is hydrogen carbonate produced and where is it controlled?
Erythrocytes produce it and the kidneys control concentration
When would the kidneys increase or decrease the concentration of hydrogen carbonate?
Respiratory acidaemia will be compensated for by the kidneys by increasing bicarbonate
Resp alkalaemia will be compensated for by the kidneys by decreasing bicarbonate
Explain what happens when acid is produced metabolically?
Acid produced by the tissues acts with hco3 producing co2 which is blown off at the lungs.
Causes a decrease in hco3 and therefore decrease in ph
A decrease in ph due to a decrease in hco3 is metabolic acididosis
What is metabolic acididosis
A reduction in oh due to a reduction in bicarbonate as it is used up with the hydrogen ions
How can metabolic Acidosis be compensated for?
Hyperventilating
How is metabolic acidosis detected?
Activation of peripheral chemoreceptors which stims resp neurones in medulla which increase ventilation and decreases pco2
If a pt is vommiting profusely, and therefore develops metabolic alkalosis, explain why hypo ventilating won’t work entirely and also why there are high levels of hydrogen carbonate in the ECF.
We vomit h ions, water and electrolytes. We cannot react bicarbonate with the h ions and therefore have an excess. We also have low blood volume. Our need to increase blood volume is greater than restoring ph. Therefore we reabsorb sodium from the cell into the blood, this is linked to bicarbonate. This also drives an increase in sodium reabsorbtion from lumen, this is linked to hydrogen being pumped INTO lumen.
The hypoventialation only works until hypoxia drive kicks in
Where is the majority of the recovery of bicarbonate achieved?
80 percent in the pct
How is recovery of bicarbonate in the pct achieved?
Driven by the sodium gradient which is established by nak atpase on basolateral membrane. This drive sodium in and hydrogen out on the luminal membrane. H reacts with bicarbonate to form water and co2 via carbonic anhydrase. Moves across memrbrane into cell. CA converts back to h and hco3 which moves with sodium into ECF
How do we recover the last of the hydrogen carbonate in the distal tubule when the tubule is hypoosmotic and therefore there is no sodium concentration gradient?
The metabolically active kidney cells produce a lots of carbon dioxide which then forms hydrogen ions and hydrogen carbonate. To maintain this forward reaction we have to buffer the hydrogen ions. So they actively secreted into lumen via h atpase. H ions are then buffed by hpo4+ and excreted as ammonia
What are the cellular responses to acidosis?
Decrease ph enhances activity of NA/h exchanger, ammonium production in PT, of Hatpase in distal and increases capacity to export hc03 from tubular cells to ECF
How do you calculate the anion gap?
The difference between the cations - sodium and potassium and the anions - chloride and bicarbonate.
Why is there normally an anion gap?
Because there are other anions that are normal but unaccounted for
When wil the anion gap increase?
If other anions from metabolic acids replace hco3- indicates that it has been replaced than an anion other than chloride.
What is the plasma ph control range
7.35-7.45
